The present invention relates to a housing for a combination current sensor and relay.
One of the trends in many industrial environments is to use an ever increasing number of electrical devices that include small motors, such as motors incorporated with fans. Typically such small motors only draw a limited amount of current, such as 1-10 amps. To provide fault detection for electrical devices having limited current requirements, a current sensor is electrically interconnected with the power cable to the electrical device to sense the electrical load current. The current sensor may include an electrical interconnection to a remotely located control panel to provide a signal to the control panel representative of the current within the power cable. It is desirable to locate such a current sensor within a housing, such as a starter housing within a substation. The current sensor or an associated relay may be interconnected to a separate starter, if desired. A relay is typically electrically interconnected between the remotely located control panel and the electrical device to receive a control signal from the control panel and in response selectively enable or disable power to the electrical device. Like the current sensor, such a relay may be located within the starter housing. In addition, the relay may function as the starter if the power rating of the relay is appropriate. Because of decreasing starter housing sizing, the relay and current sensor may be enclosed within a single unitary housing. Such a device is disclosed in U.S. Pat. No. 5,808,846, incorporated by reference herein.
Referring to FIG. 1, Functional Devices, Inc. of Russiaville, Ind., manufacturers a Model RIBXLSA combination current sensor and relay 10. Referring to FIG. 1, the device 10 includes a start/stop relay 12 that is energized or otherwise controlled by the digital output of a controller 14. Power from a power source 16 is provided by a wire 18 which is interconnected to the start/stop relay 12 of the device 10. The start/stop relay 12 is likewise interconnected to an internal sensor 20 by a wire 22, namely, a current sensor in the form of a transformer. The output of the internal sensor 20 is interconnected to a load 24 by a wire 26. The load 24 is interconnected to the source 16 by a wire 28. Accordingly, a loop for current flow is provided by wire 18, the start/stop relay 12, the wire 22, the internal sensor 20, the wire 26, and the wire 28. When the start/stop relay 12 is open, as a result of the controller 14, the power to the load 24 is interrupted (open circuit). Likewise, when the start/stop relay 12 is closed, as a result of the controller 14, power is provided to the load 24 (short circuit). Accordingly, the controller 14 may control power to the load 24 by energizing and de-energizing the start/stop relay 12. The device 10 may include a closed/open/auto switch 21 for enabling the operation of the start/stop relay 12. Other applications of the device 10, are illustrated in FIGS. 2 and 3. A solid state switch 21 measures the current level to the load 24 and provides an open/closed signal to the controller 14 based on the current level.
Referring to FIG. 4, the combination current sensor and relay 10 Model RIBXLSA from Functional Devices, Inc. is packaged in a rectangular housing 40 with a threaded opening 42 on the lower portion though which are passed a pair of wires 18 and 26. The wires 18 and 26 are connected in series with the power cable to the load as shown in FIGS. 1-3. Internal to the housing 40 are a set of four wire connectors 110 to which the control wires to the controller 14 are attached. To access the four wire connectors 110 the rear panel 44 is removed. The control wires may be passed through an opening 46 in the upper left hand side, an opening 48 in the upper right hand side, or both, as desired. The textual and graphical indication for which connectors correspond to the solid state switch 21 and to the relay 12 are provided on the back panel of the device. A set of three light-emitting-diodes 50, 52 and 54 are provided on the top of the housing 40. The right hand diode 54 provides an indication as to whether the relay is energized. The left hand pair of diodes 50 and 52 provides assistance in adjusting the set point for the current level of the solid state switch 21. When the central diode 54 is activated the current is over the trip point. When the left hand diode 50 is activated the current is under the tri point. A potentiometer that is accessed within the housing 40 when the back 44 is removed adjusts the set point for the switch 21. The switch 21 includes some hysteresis. To adjust the device 10, the potentiometer is decreased (turned counterclockwise) until the central diode 52 turns on (may already be on). The potentiometer is then increased (turned clockwise) until the left hand diode 50 turns on. Then the potentiometer is decreased (turned counterclockwise) until the central diode 52 turns on. This properly adjusts the current level. The instructions for adjusting and the meaning for the light emitting diodes are provided within the housing 40. A closed/open/auto switch 56 is provided on the left hand panel of the housing 40. Likewise, the instructions for the settings of the switch 56 are provided on the back panel of the housing 40. The entire housing 40 is secured to a wall by a set of four screws at the corners thereof.
The present invention overcomes the aforementioned drawbacks of the prior art by providing a combination current sensor and relay with an improved housing. The housing has several aspects which result in improved functionality. In one aspect, the housing includes light emitting diodes on an upper surface that indicate open circuit and short circuit conditions. In another aspect, the housing includes a securement structure for a circuit board that includes the transformer and switches for device operation, together with aligned openings therein for routing wires to external devices. In another aspect, a multiple position switch is included on the upper surface that indicates multiple modes of operation of the device. In another aspect, the housing may be assembled in multiple parts by fixing a first portion to a support, a circuit board to the first portion, and a second portion to the first portion. In another aspect, the housing is suitable for engagement to alternatively a junction box and a duplex box. In another aspect, the configuration of the upper surface provides usability advantages.